Fischer-Tropsch synthesis of lower hydrocarbons on silicalite-1 supported cobalt and cobalt-manganese catalysts is reported. The catalysts were prepared by impregnating the calcined support with the corresponding metal nitrate solutions. Co3O4 was found to be the only phase present in the manganese free catalyst, while addition of manganese favoured the formation of the mixed spinel (Co1-xMnx)(3)O-4 phase. Addition of manganese decreased the reduction temperature of Co3O4 and also presumably reduced its particle size. The catalysts showed good activity and selectivity for light hydrocarbons in the C-2-C-4 range, particularly propene and also showed very low water gas shift activity. Addition of manganese increased CO conversion rate at 250 degrees C. The alkene selectivity of the Co/Sil catalyst decreased slightly by the addition of manganese.